Warm white LEDs with high-color-rendering index (CRI, Ra>80) and low correlated color temperature (CCT<4500K) need a suitable red phosphor. Successful phosphor materials include materials such as Eu2+ or Ce3+ doped (oxy)nitride compounds, for example (Ba,Sr)2Si5N8:Eu2+ and (Ca,Sr)AlSiN3:Eu2+. However, these phosphors have drawbacks when used in certain applications since their emission spectra are broad (full-width at half maximum is approximately 75-85 nm) and a large part of the spectrum is beyond 650 nm in wavelength—a part of the spectrum to which human eyes are insensitive—which significantly reduces the lumen efficacy of LED lighting. MSxSey:Eu2+ materials show red color emission from 600 to 650 nm, and provide high lumen efficacy of LED lighting after combining with yellow or green phosphors. However, the narrow band red phosphors with general composition MSxSey:Eu are hygroscopic, and exhibit rapid deterioration of photoluminescence due to exposure to moisture (water vapor), oxygen and/or heat. Clearly there is a need for improved narrow band red phosphors with general composition MSxSey:Eu, which are compatible with coatings to protect the phosphor particles from moisture and oxygen and enable a commercially useful phosphor.
Furthermore, there is a need for red narrowband phosphors at very specific wavelengths for use in LED backlights, increasing the display color gamut, and providing more vivid colors for TV, smartphone or other consumer electronics.